Effects of heat treatment on morphology of primary α phase and hardness of B-refined Al-7Si alloy were investigated to determine the optimized heat treatment rule.The results indicate that primary α phase is converted from irregular dendrite into uniformly distributed equiaxied granular grain and then into rosette structure with holding for from 3 hours to 12 hours at 450℃

in which the ideal grain morphology can be observed with holding for 6 hours.With holding for 8 hours and increasing temperature from 300 to 540℃

primary α phase is evolved from developed dendrite into rosette and granular structure.Granular primary α phase with smaller size and uniform distribution can be observed in the alloy at 400

4

50℃

however

with holding at more than 450℃

primary α phase is transformed into irregular coarse morphology.The orthogonal analyses shows that the optimized heat treatment parameters are（540±10）℃ for 6 hours.